1. Field of the Invention
The present invention relates to an information distribution system such as a video-on-demand (VOD) system. More particularly, the present invention relates to a method and apparatus for applying conditional access impulse authorization techniques to information on demand services such as video on demand services.
2. Description of the Background Art
In an information distribution system, such as video on demand (VOD) system, an information provider (e.g., a head-end in a cable television system) must control of the distribution of requested information to ensure that only an appropriate information consumer (e.g., a requesting VOD subscriber) is able to utilize the distributed information. To provide this functionality, information distribution systems are often implemented using a conditional access system.
VOD systems providing content encoded according to the various Moving Pictures Experts Group (MPEG) standards are known. For example, a first standard known as MPEG-1 refers to ISO/IEC standards 11172, which is incorporated herein by reference in its entirety. A second standard known as MPEG-2 refers to ISO/IEC standards 13818, which is incorporated herein by reference in its entirety. Additionally, a compressed digital video system is described in the Advanced Television Systems Committee (ATSC) digital television standard document A/53, incorporated herein by reference.
MPEG-based conditional access systems typically have three main attributes: the scrambling (or encoding) of MPEG streams, the transmission of de-scrambling messages and the transmission of authorization messages. De-scrambling messages are embedded in the MPEG transport stream and used by information consumer equipment (e.g., set top terminals) to descramble the content. Authorization messages can be sent with the scrambled stream or by some other route and are used to authorize set top terminals to use the descrambling information.
Most conditional access systems support addressing authorization messages to a pre-defined individual set top terminal (STT) or groups of STTs. That is, the head end controls which set top terminals receive the authorization messages. This method is primarily used to support conditional access for premium services (such as HBO) and call ahead pay per view.
Some conditional access systems support the concept of impulse authorizations. Impulse authorizations are primarily used for pay per view events. In the impulse method of authorization, non-STT specific authorization messages are sent to all set top terminals. The set top terminal determines if the authorization message is to be used (based upon input to the STT indicative of the desires of a viewer). Thus, the head-end of such a VOD system does not know which STTs will use the authorization. Each STT using the authorization must report such use to the head-end in some manner to ensure proper billing for content that has already been presented to the viewer.
Existing conditional access systems use a schedule including a start time, an end time, channel location, and an event number to control the scrambling, transmission of descrambling messages, and transmission of impulse authorization messages identified by the event number. In parallel, set top terminals are provided with a list of pay per view events as, e.g., a menu or electronic programming guide. Each of those pay per view events has an associated event number matching the number provided to the conditional access system. When a viewer orders a pay per view event, the set top box uses the associated event number to find the appropriate impulse authorization.
Video on demand does not fit this model because the start time, the end time, and the channel location of events are typically not known in advance.
Therefore, it is seen to be desirable to provide a method and apparatus enabling conditional access to on-demand content of variable duration. Moreover, it is seen to be desirable to provide such conditional access using impulse authorizations. More generally, it is seen to be desirable to apply such impulse authorization techniques to content such that requested content may be real-time encrypted or pre-encrypted.